1. Field of the Invention
The present invention relates to a voltage control circuit for a dimmer, and more particularly, to a voltage control circuit for a dimmer that supplies a constant voltage to a lighting device regardless of a dimmer by adding a means for converting the voltage changed due to the dimmer into the constant voltage, and a dimming method using the same.
2. Description of the Related Art
A lighting device using a light emitting diode (LED) has advantages, such as long life and low power consumption, compared to existing lighting devices. However, the LED lighting device has a problem with compatibility with an existing dimmer installed according to characteristics of an incandescent. The dimmer is an apparatus that adjusts brightness of a lamp (for example, an incandescent or a halogen lamp) by varying AC input power. Since the driving range of the dimmer is diverse, it is needed to develop an LED lighting device that shows the same characteristics in all dimmers.
A problem in a conventional primary-side regulation (PSR) topology for lighting devices, as shown in FIG. 1, is that the range of a reference voltage Vref is changed according to the type of the dimmer. In the PSR topology, the brightness of an LED, that is, the light quantity is proportional to the size of the reference voltage Vref. From user's viewpoint, it means that the light quantity of the LED is changed whenever using different dimmers.